There is conventionally known a first type of developing cartridge providing a first specification and compatible with and attachable to a first type of image forming apparatus, and a second type of developing cartridge providing a second specification and compatible with and attachable to a second type of image forming apparatus as described in a prior art. The first type of developing cartridge cannot be attached to the second type of image forming apparatus, and the second type of developing cartridge cannot be attached to the first type of image forming apparatus.